- 1 cup lager beer, divided
- 2/3 cup malt vinegar or red wine vinegar
- 1/3 cup whole brown mustard seeds (about 2.2 ounces)
- 2 tablespoons dry mustard (such as Colman's)
- 1/4 cup prepared white horseradish
- 1 teaspoon coarse kosher salt
- 1 teaspoon freshly ground black pepper
- 1 tablespoon honey
- 1/4 teaspoon caraway seeds, finely ground in mortar with pestle or in spice mill
- 2 teaspoons cornstarch mixed with 1 tablespoon water
- Whisk 1/2 cup beer, malt vinegar, mustard seeds, and dry mustard to blend in small bowl. Let mixture stand at room temperature 3 hours.
- Transfer beer-and-mustard-seed mixture to blender; add remaining 1/2 cup beer, horseradish, 1 teaspoon coarse salt, 1 teaspoon pepper, honey, and ground caraway seeds; blend until coarse puree forms. Transfer mixture to medium metal bowl. Set bowl over saucepan of simmering water and whisk often until mixture thickens slightly, about 15 minutes (mixture will be thinner and more sauce-like than store-bought mustard). Transfer mustard to small saucepan and add cornstarch mixed with 1 tablespoon water; whisk over medium-high heat until mustard thickens and boils, about 2 minutes. Transfer mustard to airtight container. Cover and chill until cold. DO AHEAD: Can be made 1 week ahead. Keep chilled.
- Sold at specialty foods stores, Indian and Asian markets, and online at . If unavailable, use yellow mustard seeds instead.